How to Open Another Mailbox in Outlook

This is a detailed guide on how to open another Mailbox in Outlook.

In this guide you’ll learn:

  • How to Open Another Mailbox in Outlook Desktop Client
  • Steps to change the outlook from address
  • How to access another user’s calendar
  • How to Open Another Mailbox in Outlook Web
  • Change the from Address in the Outlook Web Client
  • How to Open Another Calendar Using Outlook Web Client

Let’s get started.

To open another user’s mailbox you will need full mailbox permissions to the mailbox. Refer to the article grant full mailbox permissions in office 365 for complete instructions.

Open Another Mailbox in Outlook Desktop Client

In this example, we will be logged in as the user ‘123 User’.  The user ‘123 User’ has been given Send As or Send on Behalf permissions to the mailbox ‘ABC User’. 

IMPORTANT NOTE: If the hide mailbox option is On, then the user trying to access the mailbox that you just gave access to will not be able to see it when they try to access it. This is ONLY the case if the user is delegated Send As or Send on Behalf permissions. To check this, in the Exchange Admin portal, make sure the Hide from Address list is not enabled.

Step 1. Open the Outlook Desktop Client

With Full Access permission given, the mailbox will automatically populate in the Outlook Desktop Client.  Please note that it may take a couple of hours for it to sync to the Outlook Desktop Client depending on how big the mailbox is.  You should see the mailbox in the left-hand side of the screen under your mailbox.

mailbox auto populate in outlook

Step 2. Click the the shared mailbox

Click on the shared mailbox to see the contents.

expand the mailbox

With this access, you can do everything the owner can do with the mailbox.  Please keep in mind that you will need to change the From address if you send emails from the ABC User account. It will default to the 123 User (since that is who we are logged in as in this example). 

Steps to change the Outlook from address:

1. Click on New Email.  Then click on Options at the top, then the … and select From under Show Fields.

add the from address outlook client

2. Where it shows 123User@activedirectorypro.com, click on From, then select Other email address.

select other email address outlook

3. You can type in the email address if you know it or click the From to open the global address book. 

from field

In this case, we will click From.  Type in ABC in the search bar and press the arrow to search for it or scroll to locate it. 

search gal for user
Click on ABC User and then click on Ok. 
select user

Click Ok again and ABC User will now be in the From Field.

from field in outlook client

You can toggle back and forth between sending emails from 123 User and ABC User as they both will be saved now when you click on From.

toggle email from address

How to Access the Calendar

To access the calendar, Click on Calendar and you will see the ABC User listed under Shared Calendars.  To view the calendar, select the box to the left of it. If you would like to hide the calendar again, just uncheck the box. 

access calendar client

Open Another mailbox in Outlook Web

In this example, we will be logged in as the user ‘123 User’.  The user ‘123 User’ has been given Full Access to the mailbox ABC User.  There are a couple of ways to do this so I will go over both.

Step 1. Log into the outlook web app

Go to https://portal.office.com and login and select Outlook.

outlook web client

Step 2. Expand the Folders

Then right-click on Folders, and select Add shared folder.

outlook web add shared folder

Step 3. Type in the mailbox

In the add shared folder field type in the mailbox that you were just given access to.

outlook web select name or email

Click on Add.

click add button

Now you will see ABC User show up in the list on the left-hand side of the screen.  Click the down arrow to access the mailbox.  With this access, you can do everything the owner can do with the mailbox. 

outlook web view another mailbox

Please keep in mind that you will need to change the From address if you send emails from the ABC User account. It will default to the 123 User (since that is who you are logged in as in this example). 

How to Change the From Address in the Outlook Web Client

1. To do this, click on New Email.  Then click on Options at the top and select Show From.

outlook web add from field

2. Click on From, then select Other email address.

outlook web add from email address

3. Now type in ABC User (the mailbox that 123 User was given Full Access permissions).

4. Click on ABC User and this will now be in the From Address. 

How to Open Another Users Calendar Using Outlook Web Client

1. Click on Calendar, then click on Add Calendar.  Select Add from the directory on the left-hand side.  Type in ABC to search for the calendar, then click on the mailbox. 

outlook web add another calendar

2. Under Add to, you can choose where to store your calendar.  In this case, I am selecting My Calendars.  Click Add. 

add calendar to list

ABC User will now have been added under your calendars on the left-hand side of the screen.  If your Add calendar menu is still up, click on the X in the upper-right hand corner.

access outlook web calendar

With a checkmark beside both calendars, you will see the schedule of both 123 calendar and the ABC User calendar.  If you do not wish to see the ABC User calendar, you can just uncheck it. 

The second option to view another user’s mailbox is to use the option to Open another mailbox. This opens the mailbox in a different window.

1. On the far right-hand side of your Outlook Web where it shows the initials, click on the circle with initials. Then click on “Open another mailbox”.

open another mailbox from web

2. After clicking on Open another mailbox, type in ABC User (the mailbox the user 123 User was granted Full Access to) in the box.

3. Click on ABC User in the list and then click Open.

The ABC User’s mailbox will be opened in a new window.   You can verify the mailbox is that of ABC User by looking at the address line.  You will see ABCUser@activedirectorypro.com in the address. 

I hope you found this article useful, if you have any questions, just leave a comment below.

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